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<a name="Machine_002dIndependent-Predicates"></a>
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<a name="Machine_002dIndependent-Predicates-1"></a>
<h4 class="subsection">17.7.1 Machine-Independent Predicates</h4>
<a name="index-machine_002dindependent-predicates"></a>
<a name="index-generic-predicates"></a>

<p>These are the generic predicates available to all back ends.  They are
defined in <samp>recog.c</samp>.  The first category of predicates allow
only constant, or <em>immediate</em>, operands.
</p>
<dl>
<dt><a name="index-immediate_005foperand"></a>Function: <strong>immediate_operand</strong></dt>
<dd><p>This predicate allows any sort of constant that fits in <var>mode</var>.
It is an appropriate choice for instructions that take operands that
must be constant.
</p></dd></dl>

<dl>
<dt><a name="index-const_005fint_005foperand"></a>Function: <strong>const_int_operand</strong></dt>
<dd><p>This predicate allows any <code>CONST_INT</code> expression that fits in
<var>mode</var>.  It is an appropriate choice for an immediate operand that
does not allow a symbol or label.
</p></dd></dl>

<dl>
<dt><a name="index-const_005fdouble_005foperand"></a>Function: <strong>const_double_operand</strong></dt>
<dd><p>This predicate accepts any <code>CONST_DOUBLE</code> expression that has
exactly <var>mode</var>.  If <var>mode</var> is <code>VOIDmode</code>, it will also
accept <code>CONST_INT</code>.  It is intended for immediate floating point
constants.
</p></dd></dl>

<p>The second category of predicates allow only some kind of machine
register.
</p>
<dl>
<dt><a name="index-register_005foperand"></a>Function: <strong>register_operand</strong></dt>
<dd><p>This predicate allows any <code>REG</code> or <code>SUBREG</code> expression that
is valid for <var>mode</var>.  It is often suitable for arithmetic
instruction operands on a RISC machine.
</p></dd></dl>

<dl>
<dt><a name="index-pmode_005fregister_005foperand"></a>Function: <strong>pmode_register_operand</strong></dt>
<dd><p>This is a slight variant on <code>register_operand</code> which works around
a limitation in the machine-description reader.
</p>
<div class="smallexample">
<pre class="smallexample">(match_operand <var>n</var> &quot;pmode_register_operand&quot; <var>constraint</var>)
</pre></div>

<p>means exactly what
</p>
<div class="smallexample">
<pre class="smallexample">(match_operand:P <var>n</var> &quot;register_operand&quot; <var>constraint</var>)
</pre></div>

<p>would mean, if the machine-description reader accepted &lsquo;<samp>:P</samp>&rsquo;
mode suffixes.  Unfortunately, it cannot, because <code>Pmode</code> is an
alias for some other mode, and might vary with machine-specific
options.  See <a href="Misc.html#Misc">Misc</a>.
</p></dd></dl>

<dl>
<dt><a name="index-scratch_005foperand"></a>Function: <strong>scratch_operand</strong></dt>
<dd><p>This predicate allows hard registers and <code>SCRATCH</code> expressions,
but not pseudo-registers.  It is used internally by <code>match_scratch</code>;
it should not be used directly.
</p></dd></dl>

<p>The third category of predicates allow only some kind of memory reference.
</p>
<dl>
<dt><a name="index-memory_005foperand"></a>Function: <strong>memory_operand</strong></dt>
<dd><p>This predicate allows any valid reference to a quantity of mode
<var>mode</var> in memory, as determined by the weak form of
<code>GO_IF_LEGITIMATE_ADDRESS</code> (see <a href="Addressing-Modes.html#Addressing-Modes">Addressing Modes</a>).
</p></dd></dl>

<dl>
<dt><a name="index-address_005foperand"></a>Function: <strong>address_operand</strong></dt>
<dd><p>This predicate is a little unusual; it allows any operand that is a
valid expression for the <em>address</em> of a quantity of mode
<var>mode</var>, again determined by the weak form of
<code>GO_IF_LEGITIMATE_ADDRESS</code>.  To first order, if
&lsquo;<samp>(mem:<var>mode</var>&nbsp;(<var>exp</var>))<!-- /@w --></samp>&rsquo; is acceptable to
<code>memory_operand</code>, then <var>exp</var> is acceptable to
<code>address_operand</code>.  Note that <var>exp</var> does not necessarily have
the mode <var>mode</var>.
</p></dd></dl>

<dl>
<dt><a name="index-indirect_005foperand"></a>Function: <strong>indirect_operand</strong></dt>
<dd><p>This is a stricter form of <code>memory_operand</code> which allows only
memory references with a <code>general_operand</code> as the address
expression.  New uses of this predicate are discouraged, because
<code>general_operand</code> is very permissive, so it&rsquo;s hard to tell what
an <code>indirect_operand</code> does or does not allow.  If a target has
different requirements for memory operands for different instructions,
it is better to define target-specific predicates which enforce the
hardware&rsquo;s requirements explicitly.
</p></dd></dl>

<dl>
<dt><a name="index-push_005foperand"></a>Function: <strong>push_operand</strong></dt>
<dd><p>This predicate allows a memory reference suitable for pushing a value
onto the stack.  This will be a <code>MEM</code> which refers to
<code>stack_pointer_rtx</code>, with a side effect in its address expression
(see <a href="Incdec.html#Incdec">Incdec</a>); which one is determined by the
<code>STACK_PUSH_CODE</code> macro (see <a href="Frame-Layout.html#Frame-Layout">Frame Layout</a>).
</p></dd></dl>

<dl>
<dt><a name="index-pop_005foperand"></a>Function: <strong>pop_operand</strong></dt>
<dd><p>This predicate allows a memory reference suitable for popping a value
off the stack.  Again, this will be a <code>MEM</code> referring to
<code>stack_pointer_rtx</code>, with a side effect in its address
expression.  However, this time <code>STACK_POP_CODE</code> is expected.
</p></dd></dl>

<p>The fourth category of predicates allow some combination of the above
operands.
</p>
<dl>
<dt><a name="index-nonmemory_005foperand"></a>Function: <strong>nonmemory_operand</strong></dt>
<dd><p>This predicate allows any immediate or register operand valid for <var>mode</var>.
</p></dd></dl>

<dl>
<dt><a name="index-nonimmediate_005foperand"></a>Function: <strong>nonimmediate_operand</strong></dt>
<dd><p>This predicate allows any register or memory operand valid for <var>mode</var>.
</p></dd></dl>

<dl>
<dt><a name="index-general_005foperand"></a>Function: <strong>general_operand</strong></dt>
<dd><p>This predicate allows any immediate, register, or memory operand
valid for <var>mode</var>.
</p></dd></dl>

<p>Finally, there are two generic operator predicates.
</p>
<dl>
<dt><a name="index-comparison_005foperator"></a>Function: <strong>comparison_operator</strong></dt>
<dd><p>This predicate matches any expression which performs an arithmetic
comparison in <var>mode</var>; that is, <code>COMPARISON_P</code> is true for the
expression code.
</p></dd></dl>

<dl>
<dt><a name="index-ordered_005fcomparison_005foperator"></a>Function: <strong>ordered_comparison_operator</strong></dt>
<dd><p>This predicate matches any expression which performs an arithmetic
comparison in <var>mode</var> and whose expression code is valid for integer
modes; that is, the expression code will be one of <code>eq</code>, <code>ne</code>,
<code>lt</code>, <code>ltu</code>, <code>le</code>, <code>leu</code>, <code>gt</code>, <code>gtu</code>,
<code>ge</code>, <code>geu</code>.
</p></dd></dl>

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